In the cytosolic subcellular fraction derived from the testes of rats, mice and human beings, the presence of a special form of adenylate cyclase has been established. This adenylate cyclase is hormone insensitive and it appears that it is either devoid of receptors, or functionally it is not coupled to commonly known hormone receptors. The objectives of this study are: 1) To determine the discrete cell population where, and the time when the enzyme is synthesized during spermatogenesis. This will be pursued by determining its presence is separated cell fractions enriched in specific cell types, and by immunochemical detection of the enzyme in tissue slices by the indirect fluorescent antibody techniques. 2) To characterize the chemical nature of the enzyme. Milligram amounts of the enzyme will be prepared and the homogeneity of the preparation will be examined by analytical gel electrophoresis, analytical ultracentrifugation and immunochemical tests. Partial amino acid sequence analysis will be performed using an automated sequencer, and the amino acid composition of the enzyme determined after hydrolysis. 3) To explore the mode of regulation of the rat testis soluble adenylate cyclase and to identify modulatory factors involved in it. The highly purified germ cell enzyme was found to interact with adenosine and also to possess hydrophobic binding sites. Studies will be carried out in which the enzyme will be reconstructed with naturally occuring lipids, divalent cations, and cytosolic factors, and the mechanism of their interaction with the enzyme delineated. 4) Furthermore, attempts will be made to delineate the relative importance of FSH and testosterone action in the seminiferous tubules during puberty, employing the germ cell enzyme as a quantitative biochemical marker.